Recently, the market for nonwoven fabrics has been rapidly increased. Above all, needs for nonwoven fabrics made of long fibers have been rapidly increased as they have both tough strength and soft touch.
On the other hand, in the field of such nonwoven fabrics, nonwoven fabrics which have higher characteristics and higher functional properties have been required, and in addition, uses and required grades are also increased. Therefore, it has been required to develop such production processes that are in cope with a production of a lot of grades, particularly, industrially, economically and fully in cope with a small scale production with a lot of grades.
Namely, in the conventional general methods for industrially producing nonwoven fabrics made of long fibers, spun bundles of synthetic filaments are taken up by a high-speed fluid and they are ejected from many spinnerets arranged in the width direction and are collected as a web on a flat net to obtain a nonwoven fabric. This is a typical method and this method has been broadly practiced in use.
However, this method is suitable for a large scale production and the cost for facilities is high. Moreover, when the production is performed by changing conditions such as weight and width, loss accompanied with the change in conditions is large. Therefore, when only a small scale production is performed, there is an inconvenience that the cost becomes higher on the contrary. Furthermore, in the method where a large number Of spinnerets are arranged, there exist limits on uniformity of webs and isotropy of the properties of the webs.
Particularly, it is generally said in producing nonwoven fabrics that difficulty in achievement of uniformity increases in proportion to the square of width (namely, when the width is doubled, the technical difficulty is squared and increases to four-fold and when the width is tripled, the technical difficulty is squared and increases to nine-fold) and a high technology is necessary in actual production for obtaining a uniform and good web with a wide width.
To aim at realization of such a high technology, for example, as a method for improving uniformity of a web, methods for improving the arrangement of spinnerets were proposed in Japanese Patent Laid-Open SHO 62-17057, 62-184168, 62-184169 and 62-184171, but a new problem that the apparatus became more complicated was brought about and it was a real condition that the problem could not be solved by any possibility.
Therefore, realization of a technology suitable for producing a number of grades at small scale, i.e., realization of a technology which makes it possible to produce a nonwoven fabric with a uniform quality efficiently and with less loss by a simpler facility, especially realization of a technology which can sufficiently cope with the need for producing a nonwoven fabric with a wide width and makes it possible to produce a nonwoven fabric with a required high quality, is strongly required recently.
As one of the processes for producing nonwoven fabrics which basically have a possibility to satisfy such requirements, Japanese Patent Publication SHO 47-43151, Japanese Patent Laid-Open SHO 48-20970, FIG. 4 of Japanese Patent Publication SHO 49-9436 and Japanese Patent Publication SHO 48-27227 propose manufacturing processes for nonwoven fabrics wherein fibers are ejected on the inner peripheral surface of a polygonal prismlike cylinder constituted by a number of moving endless belts or the inner peripheral surface of a columnar cylinder, the fibers are collected in the form of a web on the inner peripheral surface and a cylindrical nonwoven fabric was taken up from the cylinder.
However, as far as the inventors of the present invention know, it has not been actually reported up to now that nonwoven fabrics have been industrially produced by such processes which are said to be classical technologies for producing nonwoven fabrics.
Considering the reason, it is thought that in the process where the inner peripheral surface of a polygonal prismlike cylinder constituted by a number of moving endless belts is utilized, as fibers are collected on the inner peripheral surface of the polygonal prismlike cylinder, a difference is generated between collecting and piling conditions of the fiber on the peaks (the corners) and the sides in the polygonal cross section, and there exists a fatal defect that it is difficult to make a uniform nonwoven fabric, and further, constituting a polygonal prismlike cylinder with a plurality of endless belts with a good accuracy itself and transferring and taking-up a cylindrical web by using a plurality of the endless belts itself are unexpectedly and technically difficult. In the process where the inner peripheral surface of a columnar cylinder is utilized, it is thought as the reason that it is actually technically difficult to continuously take off the web collected on the inner peripheral surface without spoiling uniformity of the web and with keeping the uniformity as it is.